FIG. 17 is a drawing of the constitution of a conventional multi-nozzle ink jet head. Here, a bimorph actuator in which a diaphragm 95 and a piezo 96 are laminated together is used as a driving element.
Regarding the method of manufacturing the driving elements and the head 90, a plurality of individual electrodes 97 are formed by sputtering on an MgO substrate, not shown, the piezos 96 are further laminated on to a thickness of a few μm, and pattern formation is carried out. Then, a metal (for example Cr) that will become the common electrode cum diaphragm 95 is formed to a few μm over the whole surface, thus forming the bimorph structures. A pressure chamber-forming member (dry film resist) 93 and a nozzle-forming member 92, which are prepared separately, are joined on in alignment with the individual electrodes 97. Then, the MgO substrate is removed by etching, thus completing the head plate 90.
Regarding the operation, ink is fed to the head 90 from an ink tank, not shown, and then within the head 90, the ink is fed to the pressure chambers 94 and nozzles 12 via a common channel and ink supply channels, not shown. Driving signals are applied to the individual electrodes 97 (the electrodes corresponding to the respective nozzles) from a driving circuit, whereupon, due to the piezoelectric effect of the piezo 96, the diaphragm 95 deflects towards the inside of the pressure chamber 94 as shown by the dashed lines in FIG. 17, and ink is ejected from the nozzle 12. The ink forms dots on a printing medium, and by controlling the driving of the apparatus and the head, a desired image is formed.
With an ink jet head using such thin-film piezos, the ejection of ultra-small particles is possible, thus raising the printing quality, and moreover a semiconductor manufacturing method can easily be applied, and hence a small head with a plurality of nozzles at high density can be realized at low cost.
However, as shown in FIG. 17, in the case that the nozzle density is made high, the pressure chamber walls 93 that connect between adjacent nozzles 12 become thin, and the rigidity drops. For example, with a head having a nozzle density of 300 dpi, the nozzle pitch is low at 85 μm, and the thickness of the pressure chamber walls is 35 μm or less. This drop in the rigidity of the pressure chamber walls 93 causes a loss of generated pressure during driving, a drop in the responsiveness of ink flow, and as a result a drop in the particle formation speed and the driving frequency. In particular, if the pressure chamber wall member 93 is a resin such as a dry film resist, then the drop in the rigidity of the pressure chamber walls is marked.
To suppress these effects, conventionally a method in which the pressure chamber walls 93 are made thick, and a method in which the pressure chamber-forming member 93 is made to be a metal or the like, which has a higher rigidity than a resin, have been proposed, and as a result the rigidity of the pressure chamber walls 93 can be secured.
However, making the pressure chamber walls 93 thicker makes it impossible to make the nozzle density high from a structural perspective. Moreover, if the pressure chamber-forming member 93 is made to be metal, then it is necessary to form the pressure chamber pattern with an accuracy of a few μm at a pressure chamber depth (metal layer thickness) of a few tens of μm. This results in a high cost. With these countermeasures, it is thus difficult to achieve a high nozzle density at low cost.